Conventionally, there is known a steering control device which recognizes a lane boundary line (white line) on a road from image data captured by an in-vehicle camera which is used to capture images of a road ahead of a vehicle and controls a moving direction of the vehicle by driving a steering mechanism using an electric power steering motor (EPS motor) so that the vehicle travels along the traffic lane bounded by the lane boundary line (for example, refer to Japanese publication of unexamined patent application No. 2003-154960).
If an output torque of the EPS motor is feedback controlled so that the vehicle position follows, for example, the center line of the traffic lane with reference to the center line, the vehicle may travel with the vehicle position diverging from the center line to some extent, instead of following the center line, in the case where a lateral external force is continuously applied to the vehicle such as where the traffic lane has a pitch designed to discharge water or a side wind is continuously applied to the vehicle.
Therefore, in order to prevent this situation, a target value of the output torque of the EPS motor has been determined by an integral control with an input of a positional deviation of the vehicle from the center line of the traffic lane (the lateral displacement of the vehicle from the center line of the traffic lane).